What Kind of Gasoline Should I Use In My Model T Ford?

When the new 1909 Model T Ford first came out of the Piquette assembly plant in the fall of 1908 it was a much different world than today. Gasoline was originally produced as a by – product of kerosene production. It was marketed as a cleaning fluid and sold in drug stores and hardware stores. You could generally buy a gallon can of gasoline for about 30 cents, which sounds inexpensive, but in 2017 currency it is equivalent to about $8.07 a gallon! We have much better quality gasoline today, and it is much cheaper.

Service stations as we know them today were not around until some time after WWI. Instead, as it became more common to see automobiles taking the place of the horse drawn wagon, we started to have roadside gasoline pumps. Often they were in front of the drug store where the gallon cans of gas had previously been sold. Other common places were in front of blacksmith shops, car dealerships, and general stores.

Gasoline in 1908 was generally better quality than gasoline a few years later. As a result, Ford lowered the compression of the Model T Ford in late 1912 model year by increasing the combustion chamber size slightly on the “low” cylinder head. Another change made in 1912 was changing the camshaft design to reduce cylinder pressure, again in response to decreasing gasoline quality.

Typical gasoline available in 1912 would be rated about 60 octane by today’s standards of R/M. Octane is the resistance of gasoline to preignite, also sometimes known as “spark knock”. More information on octane can be found at the US Department of Energy website:http://www.fueleconomy.gov/feg/octane.shtml

Octane rating necessary for good operation of your Model T Ford is anything above 70 octane. In general this means the cheapest gas that you can buy is fine. Are there any additives that need to be used, like octane boosters, lead additives, or Marvel Mystery oil?

In a word, no.

The Model T Ford has a four stroke cycle engine. This type of engine has oil in the crank case for lubrication, and fuel is as oil free as possible. This type of engine suffers if any oil is added to the gasoline supply or if oil enters the combustion chamber because of worn rings or worn valve guides. Any oil that enters the combustion chamber causes soot to be increased during the combustion process. Soot deposits become caked on the rings and cylinder head. This results in hot spots that can cause preignition and irregular combustion events. This is why additives such as Marvel Mystery Oil are easily dismissed as of no use, because on scientific terms they (any type of oil or oil based additive in the gasoline supply) are proven to be harmful.

What about octane boosters, lead additives, or Sta – Bil? Again, the Model T is a very low compression engine, about 4.7:1 for the pre – 1913 cars, and about 4.5:1 for cars and TT trucks made from 1913 – 1927. In stock form you don’t need anything except the cheapest 80 octane unleaded gas that you can buy.

My experience with Sta – Bil is not too impressive. In the 1990’s I was working for a fine fellow named Fred Tycher maintaining his collection of antique and classic cars. Fred had a Ruxton, several Delages from the 1930’s, about 20 Pierce Arrows from all model years, several collectible Thunderbirds, a Model T, a Model A Ford, some various cars from the 1950’s, etcetera. Fred liked to look at the cars mostly, driving them was very occasional. He might drive his favorite three or four cars once or twice a year. Needless to say, bad gas was a big problem, and more often than not my duties included rebuilding a carburetor or fuel pump, or removing a gas tank so it could be cleaned professionally. A friend recommended Sta – Bil, and Fred had us conduct a test of sorts. I rebuilt the carburetor on his 1937 Pierce Arrow town car, and had the gas tank vatted at the local radiator shop. The fuel pump received a new diaphragm, and the gas lines were replaced with new tubing. The gas tank was kept full with Sta – Bil added in the recommended ratio. Then the car was driven a few times and put away in the warehouse for several years. About 1997 we tried to start the car and no gas was reaching the carburetor. The gas had again gone bad in the tank.

My recommendation is: if you are not going to drive your collector car for the next few months is to drain the gas and use it in your modern car.

But what about lead – my buddy in the trailer park says that lead cushions valves? This is a common old wives tale. Tetraethyl lead is a liquid additive that became common in automotive gasoline following World War II to raise octane levels. It was developed in the years before the war to make it cheaper to produce high octane fuels for combat aircraft. Higher octane fuels are more resistant to pre – ignition. This allows engine designers to  do things that increase engine power. First, cylinder pressure can be raised which can be accomplished in several ways including higher compression ratio, more aggressive camshaft design, and supercharging the intake air / fuel mixture. Second, timing advance can be increased (made earlier) to effect more efficient fuel burn, which increases both power and fuel economy. The old wives tale is based on the fact that valve seat wear is dramatic if lower octane fuel is used in an engine designed for high octane fuel. The trailer park theory being that lead must somehow “cushion” the exhaust valve. In reality the lower octane fuel will require less spark advance. This “later” timing causes incomplete combustion of the fuel / air mixture. The inefficient combustion process results in superheated (and still burning) combustion gases going out the exhaust valve as it opens. This in turn leads to a very hot, very soft, and very malleable exhaust seat. Now you know the real story.

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